Great icon, but I dislike the blockiness of the leaves. Maybe try making it more of an oval shape?
Nice. A backlight would help it, plus theres a slight problem with lighting but I can't pin it
It seems that pixel art is just made for trees, doesn't it? Or maybe the other way around 
But really, trees are so wonderful in pixel art. Every time I see them this well done it makes me want to try to make another. I like the unbalanced sides that Delicious brought up, it makes it a little more believable. Fantastic work.
That foliage is really nicely done.
The palette is pretty straightforward and doesn't really give a feeling of depth, IMO. I think if you used more purple/blue in the darker shades and added bit more saturation to the upper ranges it would give the piece a more three-dimensional feel to it.
I think that's excellent for 8 colors, I like the palette and the overall style (even if it could use more contrast).
I think it would look good on the left side of a road, with a mirrored version for the right side.
Beautiful tree! I just have to agree that the palette could be more interessting and the trunk is to simple. But keep up the good work 
Wow thanks, now it's much more better and i thought that leaving the trunk simple would capture the attention on the foliage, well, silly me.
@Mrmo Tarius
Naa, they are just "tetris blocks".
@Delicious
My first SERIUS attempt AFTER reading/studing a bunch of tutorial and stuff.
The leaves' texture is rendered beautifully.
The only thing I miss here is a bit more interesting pallete, and the trunk looks slightly boring compared to the lavish foliage. I tried my hand at it:
http://i.imgur.com/Cil4d.png
I tried making the trunk a bit more detailed.
I really like it! The trunk feels a little to simple compared to the leaves though. Maybe add a highlight color.
Beautifully done. Amazing that it's your first attempt at a tree. It's a bit unbalanced comparing both sides though, but not all trees are perfect so that can be ignored. :P
Amazing textures!